VMFS datastore showing greyed out, inactive and unmounted

I’ve been having “fun” recently with VMware storage issues following a temporary loss of power to one of my two EMC Clariion CX4-480 SANs. The power outage was expected, and the SAN was shut down before the electricity was lost. However, ever since I’ve been periodically getting hosts greying out in the vSphere client. They’d eventually come back to life again, and the VMs running on them didn’t seem affected – though they did grey out in vSphere client too and were thus not manageable, but it was worrying – something wasn’t happy.

One host (they’re all running ESXi 5.0 update 2, build 914586) in particular had had several of these issues, more so than the others. So this morning, when it was looking normal, I decided to try putting it into maintenance mode (which worked) and then rebooted it once all the VMs had been moved off it.